With Shadow Text you encrypt a message right inside the keyboard – with a password only you and the other person know. You can then share the encrypted text in any app (messenger, e-mail, forum). On the way nobody sees the content, only a block like [ShadowText …]. Only someone who knows the password can read it.
How to use it:
• Put the Encrypt text and Decrypt text functions on keys – or use the Quick Settings tile or Android's process-selected-text action.
• Type your message, enter a password – your Shadow Text block is ready.
• The other person pastes the block, enters the same password and sees the plain text.
Why you can trust Shadow Text:
• Everything happens on your device. Encryption runs entirely locally – nothing is sent to any server. Keyboard Designer requests no permissions at all and needs no internet connection for this.
• Proven, strong encryption. It uses AES-256 in GCM mode – a worldwide standard, not a home-made scheme. The key is derived from your password with PBKDF2 (HMAC-SHA256, 200,000 iterations), which makes guessing extremely hard.
• Your password is never stored. It never leaves your device and is kept nowhere – the key is only computed from it when needed.
• Tampering is detected. Every message carries an authenticity check. If the block was altered or the password is wrong, decryption fails clearly – instead of silently producing garbage.
• Privacy in the details. Every message uses a fresh random value, so identical texts never produce the same block.
• Your clipboard stays protected. Decrypted text is not copied to the clipboard automatically – only if you explicitly choose to. The clipboard is system-wide: other apps could read it, and many devices also keep a clipboard history. And if you do copy, the clipboard is automatically cleared 60 seconds afterwards.
In short: only the encrypted block ever leaves your device – and only someone with the password can read it.
Does it hurt that the method is open and can be rebuilt?
No – quite the opposite. Security never depends on the method being secret, only on your password (Kerckhoffs's principle). Someone who knows the method but not the password cannot read your text – they would have to guess the password, which PBKDF2 with 200,000 iterations makes very expensive. And it is nothing home-made: it is the same, globally proven technology. AES-256 protects, for example, HTTPS websites, Wi-Fi (WPA2/WPA3), messengers and disk encryption – it is a standard of the US authority NIST and is even approved for classified government data. PBKDF2 is used, among others, by password managers and for Wi-Fi passwords. That such methods are open is a sign of quality.
Is it also safe against quantum computers?
Shadow Text is well positioned here. It uses no RSA or ECC, so the well-known quantum attack (Shor's algorithm) that breaks such key methods does not apply at all. Against AES-256 the relevant quantum attack (Grover) effectively halves the strength to about 128 bits – and 128 bits are considered practically unbreakable even with quantum computers. A strong password remains the decisive factor.
What if I forget the password?
Then the message is lost for good. There is no backdoor and no recovery – which is exactly what makes it secure: nobody can bypass it, not even the developer. So keep important passwords safe.
What does the other person need to decrypt?
When you send a Shadow Text block, the recipient also needs Keyboard Designer (with the "Decrypt text" function) and the password. Tip: agree on the password through a different channel than the message itself – for example in person.